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At least 145 records · Page 8Linked to original sources
PubMed1991

[Objective assessment of disorders of visual perception following unilateral vestibular loss. Studies of the so-called Dandy symptom].

Visual ability and compensatory eye movements during defined vertical oscillation were investigated in 20 patients with unilateral lesions of labyrinthine function and in 20 normal subjects. Oscillation frequencies were performed at the rate of 1 to 1.5 Hz with an amplitude of 5 cm, comparative to head locomotions of a running person. In synchronism with this, the visual function was tested with Landolt rings. Patients complaining of subjective visual disturbance during walking and running, also presented a measurable blur of vision under test conditions. In addition, eye movements were recorded and classified into three types. However, these eye movements showed no relation to gaze function. Our results suggest that the otolith-ocular reflex may participate in adjusting the vertical eye position during vertical stimulations at low frequencies. The effect of visual disturbances in patients with labyrinthine lesions is explained by the "efference-copy" initially described by von Holst. The efference-copy is responsible for the neutralisation of provoked retinal perceptions.

Adult↗
PubMed1990

Visual perception of surface curvature. The spin variation and its physiological implications.

In the context of the models of structure from motion visual processing, we propose that the optic-flow field is a source of information for the perception of the curvature of a smooth surface in motion. In particular, it is shown how the spin variation (SV), a second spatial derivative of the retinal velocity field, is mathematically related to the curvature of the surface. Under the hypothesis that the visual system relies on SV to analyse the structure of a moving surface, a neural scheme for SV detection is proposed and psychophysical predictions are developed. Results obtained on artificial images show that the SV scheme presents a rather weak sensitivity to noise in conditions of low image velocity.

Computer Simulation↗
PubMed1989

Transient impairment of visual perception induced by single interictal occipital spikes.

We have previously reported that focal occipital interictal epileptiform discharges (spikes) cause transiently prolonged reaction time (RT) and increased nonperception of stimuli, especially in the visual field contralateral to the spike. One subject with very frequent spikes was capable of carrying out a visual recognition task along with the RT task. During central fixation, computer-generated random digits were flashed for 150 ms at random locations on a screen. Some stimuli were delivered during spikes, by means of an amplitude-threshold trigger, whereas control stimuli were delivered at random times between spikes. Following each stimulus, the subject had to press a button for RT and then report the digit perceived. There was a statistically significant increase in nonresponse rate (nonperception) during spikes compared to controls, and this effect was maximal contralateral to the spike. Moreover, among the responses, perceptual accuracy (correct vs incorrect) was significantly impaired during spikes, again predominantly in the visual field contralateral to the spike. Thus, not all focal interictal spikes are necessarily "subclinical;" at least some induce a transient cortical dysfunction of the same kind as produced more enduringly from a structural lesion in the same location. These findings may have clinical relevance in patients, especially children, with very frequent epileptiform discharges and higher cortical dysfunction.

Action Potentials↗